This invention relates to the replication of microstructure-bearing surfaces, and more particularly to a genus of resinous compositions capable of such replication.
Microstructure replication in resinous surfaces is of importance in such diverse technical fields as the fabrication of traffic signs, in which reflectivity is provided by cube-corner embossed sheeting; the production of Fresnel ophthalmic lens elements and flexible video disks; and the fabrication of xe2x80x9cbrightness enhancementxe2x80x9d or xe2x80x9clight managementxe2x80x9d films (hereinafter sometimes designated xe2x80x9cLMFxe2x80x9d for brevity) for liquid crystal displays. For replication purposes, it is necessary that the resin have optimum physical properties, including a glass transition temperature (Tg) high enough for shape retention during storage and use and viscoelastic properties facilitating shaping, typically by molding, and long-term shape retention which includes the microstructure aspects of the shaped articles. Suitable viscoelastic properties include moduli in the glassy and rubbery states within certain ranges, as well as suitable transition temperatures between those states.
Many suitable resinous compositions for the replication of microstructure are disclosed in the patent literature. A patent whose disclosure is generic to a large variety of such compositions is U.S. Pat. No. 4,576,850. The compositions described therein are characterized by xe2x80x9chardxe2x80x9d and xe2x80x9csoftxe2x80x9d segments or moieties in combination with radiation-polymerizable moieties. Most often, all three of these types of segments are present in the same molecule. A key feature of the xe2x80x9chardxe2x80x9d segments is the presence therein of cyclic (i.e., carbocyclic or heterocyclic) groups. Later-issued patents frequently make reference to U.S. Pat. No. 4,576,850 for its disclosure of suitable polymeric compositions and precursors therefor.
It is of interest, however, to develop additional resinous LMF materials not disclosed in the above-identified patent or other publications.
The present invention is based on the discovery of a genus of acrylic-based resinous materials having excellent properties for the fabrication of LMF""s and other articles having microstructure.
The invention includes articles which are radiation curable to optical resinous articles having surfaces with a replicated microstructure comprising a plurality of utilitarian discontinuities having an optical purpose, said optical resinous articles having a glass transition temperature of at least 35xc2x0 C. Also included are the cured optical resinous articles so prepared.
Said radiation curable articles are free from carbocyclic and heterocyclic polymerizable moieties and comprise:
(A) at least one monofunctional acrylic monomer selected from the group consisting of:
(1) at least one monomeric t-alkyl (meth)acrylate,
(2) at least one monomeric N-substituted or N,N-disubstituted (meth)acrylamide and
(3) at least one C1-8 primary or secondary alkyl (meth)acrylate;
(B) at least one multifunctional (meth)acrylate or (meth)acrylamide monomer;
(C) optionally, at least one oligomeric multifunctional (meth)acrylate; and
(D) at least one photoinitiator.